This invention relates to a method for rotationally driving a gear material when the gear material is cut using a hob, and a gear thus hob machined.
As a method for rotationally driving a gear material when the gear material is gear cut machined using a hob, there has heretofore been employed a method in which a carrier is fixedly bolted to the outer periphery of a gear material so that the gear material is rotationally driven through the carrier, or a method in which a plurality of wedge-shaped projections are formed on an end face of a drive shaft of a gear hobbing machine in such a manner as to extend radially with respect to an axis thereof so that a rotational force of the drive shaft is transmitted to the gear material through the projections which are caused to bite into the end face of the gear material, for example.
In the first-mentioned method, the transmission of a rotational force between the carrier and the gear material is performed by only friction between the gear material, and the carrier and the bolt under the effect of a tightening force of the bolt. Therefore, it is difficult to transmit a large rotational driving force to the gear material. For this reason, a heavy cutting using a hob is difficult to perform and a gear cut machining cannot be performed efficiently.
On the other hand, in the second-mentioned method, a large rotational force can be transmitted to the gear material because the projections are caused to bite into the gear material. However, other problems are encountered in that recesses are left on the end face of the gear material as a trace of the projections bitten into the end face, and that the peripheral area of the recesses is swollen. For this reason, it is necessary to remove the swollen area when the gear is of the type that the end face of the gear is used as in a planet gear of a differential gear assembly described in Patent National Publication (Tokuhyo) No. 502713/1994, for example. As a consequence, the number of process is increased to that extent, thus resulting in decrease of gear manufacturing efficiency. Moreover, even if the swollen area is removed, the recesses are left as they are. To remove those recesses, a great number of processes are required. As a consequence, gear manufacturing efficiency is further decreased.